SILICIDE FORMATION AND PHASE-SEPARATION FROM CU/NB AND NB/CU BILAYERS ON SILICON

Electron beam evaporation was used to produce Nb/Cu and Cu/Nb bilayers on silicon. The phase sequence and morphology were investigated as a function of annealing temperature in the temperature range between 200-degrees-C and 800-degrees-C, using Auger electron spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction, and transmission electron microscopy. Independently of the sequence of deposition, the phases Nb3Si and Nb5Si3 are the two first niobium phases to be formed as a very thin layer at the Nb-Si interface. However, there is evidence that the reaction between niobium and silicon depends strongly on the presence of copper at the Nb-Si interface. The unusual coexistence of Nb5Si3, NbSi2 and niobium phases was also observed. The formation of the ternary phase Nb5CU4Si4 was detected after annealing Cu/Nb at 700-degrees-C and Nb/Cu at 800-degrees-C. In the latter case the NbSi2 and Cu3Si + Cu4Si phases were formed through a layered growth process.